Atari 7800

Unable to play NTSC carts on PAL systems, and vice versa

Due to the fiasco surrounding the unlicensed pornographic title Custer’s Revenge on the Atari 2600, Atari put a lot more thought into a system that would only allow games that they deemed appropriate able to run on their system. To this end, they invented a digital signature protection method, which prevented unauthorized 7800 games from being played on the system. How it basically worked was that the 7800 would look at a cartridge when loaded, and calculate a checksum based on the ROM code and a secret signing key known only to Atari. It would then compare the result with a stored value on the cartridge. If the two did not match, the cartridge would not boot in 7800 mode, falling back instead to the 2600 backwards-compatibility mode on the console, the logic being if it wasn’t a valid 7800 title it must therefore be a 2600 game.

However, they decided not to include this “feature” on the PAL 7800, instead using various heuristics to determine the cart type, due to the United States having export restrictions on anything involving cryptography at the time. As a result, PAL and NTSC 7800 games are fundamentally incompatible with each other – the only way to play NTSC 7800 games on a PAL television is with an NTSC console. So few games were produced for the system a modchip was never made.